Doug and Heather Carter have had raw sewage spew on to their Dargaville property at least once a year since they moved there 25 years ago.
An apologetic council is unable to explain the stinking mystery and why the sewerage line regularly spills on to their property.
On one occasion, sewage came up through a downstairs toilet and covered the basement floor - ruining carpets, drapes and furniture.
It has happened three times since last December and the Carters say they live "waiting for the next time".
Kaipara District Council operations manager John Burt said the council had put significant work into trying to resolve the problem in recent years.